I. Field of the Invention
The present invention is directed to forms for concrete pedestals which may be used to mount cantilevered structures. More particularly, the present invention is directed to a pre-fabricated concrete form work for mounting overhead cantilever signal arms, such as railroad cantilevers, whose form work, including plyform panels, is left in place when the foundation hole is back-filled.
II. Description of Related Art
Cantilever arms are commonly used when a traffic signal or the like is placed over the traffic path, such as a roadway, highway, or railroad. Such cantilever arms are typically supported by a mast that is bolted to a concrete pedestal having four large bolts embedded therein which protrude from the top of the pedestal a few inches. The nominally horizontal cantilever arm is fixed to the mast.
The concrete foundation for cantilevers is typically prepared in one of two ways. First, a hole is dug in the ground for receiving a cylindrical pipe, which may be steel or fiberboard. The pipe may be about 36" (91.5 cm) in diameter and several feet or a few meters deep. An auger drills a hole that the pipe is seated in. The pipe is then shored up against the sides of the hole, and if necessary, reinforcing bar is placed inside the pipe, and the mounting bolts are held in the form work with the threaded ends protruding from the top of the form work. Then, the form work is filled with concrete. This type of cantilever foundation is unacceptable in many applications because the columnar foundation rotates in the soil when winds subject the foundation to twisting moments. This deficiency can be overcome only by using a foundation eight to ten feet deep (2.5-3 m), depending upon soil and load conditions. A columnar foundation this deep, however, is very expensive.
Alternatively, and typically, a large hole is dug in which a conventional form work is erected. These form works tend to be cobbled together from whatever material is handy without any standardization of the structure or procedure.
In general, however, the following process is employed. First, a hole substantially larger than the foundation is dug. A base is laid out with reinforcement steel bars and a plurality of upstanding dowels is attached to the mat by welding, tying or the like. Each dowel typically is a three-fourths inch (1.9 cm) diameter steel rod seven feet (2.1 m) in overall height and includes a J-hook on its lower end, which becomes embedded in the base. Typically, about eight dowels are used in each foundation. These dowels provide the physical connection between the lower, or base portion of the foundation, and the upper or pedestal portion of the foundation.
While the base or mat sets, a wooden box that will hold the concrete for the pedestal is constructed outside the hole. Then the requisite network of reinforcing bars is assembled about the dowels, using welds or tie-wires and the like to hold the bars in place, forming a reinforcing cage. When the reinforcing structure is complete, the box is lifted by a crane and set down over the reinforcement bar cage.
Then the box is leveled and squared. When in proper position, the box is braced against the sides of the hole to prevent it from shifting when the concrete is poured. Frequently, this requires shoring up the hole, particularly in sandy or loose soil. In such soil, this step alone can take several days. The step of bracing the box usually requires two to three hours of work and requires two men to be in the hole throughout this period, which is quite dangerous because the holes are normally not fully shored up, creating the possibility that the hole will collapse on the workers. There is no physical connection between the box and the reinforcing cage--they are independent systems.
Anchor bolts are then temporarily fastened to the box. Each anchor bolt is typically a 11/2" (4 cm) diameter steel bar about four feet (1.25 m) long with a J-hook in the lower end and a straight, threaded upper end. Four anchor bolts are usually used. They weigh about 70 pounds (32 kg) each. The anchor bolts typically are inserted through holes in a plank, such as a 2".times.4" (5.times.10 cm) that is laid across the top of the box, and a nut is threaded onto the upper end of each anchor bolt so that they hang vertically within the box. The heavy work pieces make construction of a cage on the outdoor job site tedious, difficult, fatiguing and dangerous.
Next, the box is filled with poured concrete, which is allowed to set for several days. Then workers return to the site, climb down into the hole once more, and dismantle the box. Then the hole is filled, or back-filled, and the site is cleaned up, and a mast, typically having a cantilevered arm, is bolted to the anchor bolts. Under good working conditions, it takes a crew of three men about two full days to construct the box, about two days to build the reinforcing bar network or cage, which requires cutting, bending, tying and welding the reinforcement bars together. Typically, it takes about one and one-half weeks of nearly continuous activity by the crew to install one such cantilever arm foundation for a railroad cantilever signal arm. Thus, the typical prior art process is time consuming, expensive, and dangerous.
Therefore, a need exists for a form work for foundations for cantilevers and a method of making such foundations that can be installed more quickly; that is safer to install; that is cheaper to install; that reduces the level of skill required by the installation crew; that does not need to be braced in the hole because the form work is self-supporting; that produces a foundation that is ready to use sooner than the prior art.